Mutations of a single gene, ATM, cause the recessive disorder ataxia telangiectasia (AT). AT is a multisystem disease characterized by progressive neurodegeneration, immunodeficiency, tumor susceptibility, gonadal atrophy, and radiosensitivity. Recent cloning of the ATM gene has made it possible to study the basics of the pleiotropic effects of ATM. Using several polyclonal and monoclonal antibodies specific for ATM protein product, we have demonstrated that the ATM protein product is predominantly a nuclear phosphoprotein, is an authentic protein kinase, and is associated with several potential downstream effectors including a non-receptor tyrosine kinase and DNA recombination/repair proteins. Among all symptoms, neurodegeneration is most devastating to patients with AT. The goal of the proposed studies is to determine the mechanism by which these downstream effectors of ATM enhance neuronal survival and to establish model systems for future intervention of ATM-mediated neurodegeneration. There are two specific aims: 1. Molecular analysis of ATM-induced signaling events required for neuronal survival. We will first address whether one of the effectors of ATM, c-abl and NF-kB, play a role in neurodegeneration using neuronal cell lines and primary cerebellar cultures. To identify additional signal pathways, we will express dominant-inhibitory forms of ATM in neuronal cells to characterize the phosphorylation events that may be linked to neurodegeneration in ATM-deficient cells. We will also study the cellular localization of ATM during the cell cycle and upon DNA damage using the green fluorescent protein and ATM fusion protein. We will identify new components of ATM signaling pathways in neuronal cells using multiple approaches to detect ATM-associated proteins. Finally, primary mouse embryonic fibroblasts with known mutations will be studied to confirm the regulator and effector relationship between ATM and other specific proteins. 2. Studies of neuron-glial cell interaction in ATM- mediated neurodegeneration and protective effects of anti-apoptotic genes. Animal models will be used to test if progressive neurodegeneration is manifested by defects in both neuronal and glial cells. Whether gene products that promote cell survival thwart disease progression will be tested.